THE PHENOMENA OF MATURATION IN PROTOZOA 165 



divisions in protozoa, particularly in the simpler forms, bring such an 

 explanation almost to the limits of reductio ad absurdum. It is highly 

 probable that many of the so-called "reducing divisions" which dif- 

 ferent observers have noted in protozoa are not to be interpreted in 

 the same way as in metazoa. Indeed, there are but few instances 

 where chromosomes, using the term as applied to metazoan cells in 

 division, are formed, and too frequently suspicions are aroused that 

 the observer is influenced by what should be found according to 

 metazoan standards. The granules of chromatin, for example, appar- 

 ent after the technical processes which appear to be necessary in using 

 the Giemsa stain or any of its modifications, have been generally, but 

 erroneously, interpreted as chromosomes. Not only is there an entire 

 absence of the preliminary processes which characterize chromosome 

 formation in higher animals and plants, but these definite granules 

 cannot be demonstrated after use of the careful cytological methods 

 of fixing and staining that are used for tissue cells. Such "chromo- 

 somes," appearing only after use of what Moore and Breinl have 

 characterized as a "barbarous technique," can only be regarded as 

 artifacts, and the various descriptions of reduction in number of such 

 granules cannot be accepted until verified in every detail after the use 

 of methods whose reactions have been fully tested. On the other 

 hand, there is sufficient a priori reason for the belief, and numerous 

 observations to prove, that some process akin to reduction of chromo- 

 somes of higher types of germ cells occurs in protozoa, and these must 

 be taken into consideration in any attempt to explain the biological 

 significance of the phenomenon. 



In higher animals and plants the number of fully formed chromo- 

 somes is primarily reduced to one-half, not by division of the nucleus, 

 but by fusion of the chromosomes two by two. Tetrads are then 

 usually formed by transverse division of the double chromosomes. 

 Separation of the tetrads and distribution of their four parts is then 

 accomplished by two divisions of the cell, resulting in four functional 

 spermatozoa in case of the male, and in three polar bodies and one egg 

 in case of the female. Two maturation divisions are thus character- 

 istic of all higher types. 



It is quite remarkable, and not without significance, that two 

 rapidly following divisions of the nuclei characterize the preliminary 

 phases of fertilization in many different kinds of protozoa. They are 

 not necessarily connected with the two kinds of chromatin and do not 

 bring about an elimination of the chromidia from the idiochromidia 

 of the cell, for the double division not infrequently occurs after such 

 elimination has taken place. Thus, in cases of autogamy cited on 

 page 141 the nuclei formed from the idiochromidia in Entameba 

 coli and Entameba muris divide twice, one-half degenerating each 

 time, before the fertilization nuclei are mature (p. 142). In Adi- 



